Carbon tetrabromide → 3-(2,2-Dibromoethenyl)-2,5-dimethoxytetrahydrofuran

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A mixture of Zn powder (1.65 g, 25.0 mmol), triphenylphosphine (6.54 g, 25.0 mmol), and CBr4 (8.30 g, 25.0 mmol) in dry CH2Cl2 (40 mL) was stirred at ambient temperature. After 24 hours, 2,5-dimethoxy-tetrahydrofuran-3-carboxaldehyde (2.00 g, 12.5 mmol) was added and an exothermic reaction ensued. After 30 minutes, pet ether (100 mL) was added and the resultant upper layer separated. The lower layer was twice diluted with CH2Cl2 (50 mL) and pet ether (50 mL), and the upper layer reserved. The combined upper layers were combined, passed through a pad of SiO2, and concentrated under reduced pressure at 30° C. or below to give 2.18 g (55%) of 3-(2,2-dibromoethenyl)-2,5-dimethoxy-tetrahydrofuran as a volatile colorless oil, which was a mixture of diastreomers by 1H NMR and used immediately without further purification.

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